DE-CATS

[cossiemetro]

i'm thinking of fitting some de-cats probably the linked ones anybody fitted them and had a remap DID IT MAKE A LOT OF DIFFERENCE AND DOES IT SOUND DIVINE
it would be nice to liberate a bit more power also how did you get on when its MOT day

[Cyclone1]

Just fitting the linked de-cats alone will improve the sound, it will be louder than before although not quite as loud as having normal de-cats on tickover, however once you put your foot down they sound every bit as loud as normal de-cats. The bonus is that the linked de-cats may give you a bit more bhp, this will be more apparent if you have a re-map, this should see you up at between 375-390bhp.

At MOT time you simply swap the linked de-cats over with the cats, and then back again once the car has passed. This helps maintain the life of your cats which can be very expensive to replace.

Jules.

[cossiemetro]

cheers for that the more bhp the better the sound is a bonus

[longbow]

Out of curiosity has anyone successfully passed an MOT emmissions test WITHOUT cats fitted? I think its possible if the engine is in tip top shape and tune. Armed with Julian64's info on Cerb emmissions test requirements, I think I'll give it a go....

[350matt]

I've just managed to get mine through an MOT but it needed a bit of set-up and the cats fitting and it was close, the testing station had the latest computerised gear and depsite me waving my info about cerbys having some exemption he just waved if off with 'if its different then it'll be in the database the computer uses' so mine was subjected to the normal limits for 1998 cars and it passed!

Just...........

needless to say the cats have been removed again and put into hibernation for next year.....

Interestingly enough when I asked Jools about liking the de-cats he was of the opinion that don't do it to the 4.2's unless your're going to re-map it. As the one chap he knows of who has done it on a 4.2 ended up having a bit of a flat spot due to the fuelling leaning out

Matt

[trackcar]

Got a rechip for that now Matt that gets sent out with each set of linked decats. Interestingly it needs about an extra 30% of fuel around throttle sites 2-5 at 1500-1750 rpm. massive airflow increase at that point from fitting the linked decats for some reason...

[longbow]

Shame it isn't a wee bit higher in the rev range Joolz

[350matt]

but does it increase the power as well on the 4.2's?
How much is just the chip?
Matt

[HarryW]

How do the links work chaps, I understand the benefits for an odd firing 'normal' V8 of X linking the banks. However my understanding (or not ) that the flat plane AJP8 was that is effectively two 4 pots working together. The theory being if the exhaust is right for the single 4 pot it is right for a single bank of a flat plane V8

[350matt]

Aah but any large change of area on the primary pipe will create a 'reflection' of the pressure wave and give a tuning effect similar in effect ( but not strength) to running a shorter pipe, consequently this partial reflection will boost power in the rev - range for that length and the cam duration
see
http://auto.howstuffworks.com/framed.www.nightrider.com/biketech/calc_exhaustlength.htm


Matt

[cossiemetro]

jools did you read my e-mail ????
and don't the gt-40's crossover or link on there exhaust and give's more power ??

[trackcar]

350matt said:

but does it increase the power as well on the 4.2's?
How much is just the chip?
Matt

Sinlge figure hp increases at the top end Matt .. the chip is a freebie with the linked decats as i only change the fuelling where there's a problem to get it back to lambda 1 without excessive adaptive trim .. at the top end you're adding say 5bhp to a 360bhp engine, the fuelling change isn't significant

[HarryW]

350matt said:

Aah but any large change of area on the primary pipe will create a 'reflection' of the pressure wave and give a tuning effect similar in effect ( but not strength) to running a shorter pipe, consequently this partial reflection will boost power in the rev - range for that length and the cam duration
see
http://auto.howstuffworks.com/framed.www.nightrider.com/biketech/calc_exhaustlength.htm


Matt

Agree but the linking at the cat position is past the primaries and secondaries so in effect is the main exhaust, for a 4 pot optimising lengths/bores, matching them and blending them I understand benefits, I can't understand just how efectively linking two 4 pot exhaust systems work as a single system. I'm not saying it doesn't work as the figures speak for themselves I just wondered how it did it .

[Steve_T]

Possibly it works because the standard system is just a bit too small a bore? With the firing angle of the AJP, it leaves me wondering whether a slightly larger bore system is the better choice (although this option obviously has a correspondingly higher price tag).

Steve.

[caduceus]

I decatted my totally standard Cerb (which I nearly sold a while ago because it just was'nt doing it for me) last Saturday, and hav'nt looked back.

Drove back from Hampshire yesterday and scared half the population on the M25
BANG! crackle crackle BANG BANG pop pop pop!!

Get it decatted asap

[cossiemetro]

i had a rough measure of mine and they are about 17"-17.5" long pipe section not the actual cat itself does that make sense ?? whats the other size is there a big difference??
and it looks like the linked de-cats+chip is the way to go